adb.exe is a program which is most likely NOT a virus. So, if adb.exe is on your system, it is most likely ok, and will NOT be a cause for concern. Even if your system is clean, it is still recommended to purchase a well-known antivirus with a good detection rate, in order to yourself your PC against potential security problems.
Normally, this application is located in C:\Program Files (x86)\HTC\HTC Sync Manager\HTC Sync\adb.exe.
The MD5 fingerprint for this program is 5aa2ef905ae19437f57311a1e7afa41f.
This application is NOT a Windows service. This is very good.
This exe runs in 32-bit mode. It does not use the full power of modern computer CPUs. This ordinarily happens because the authors did not bother to upgrade it to 64-bit code.
adb.exe has a digital signature. Nowadays the large majority of serious software applications are digitally signed.
The digital signature attached to adb.exe is valid. This is very good.
Digital certificate name: Nero AG
Certificate's issuer name: Symantec Class 3 SHA256 Code Signing CA
This executable does NOT have an uninstall routine stored in registry.